If you are one of the millions of Americans contributing money to tsunami relief, tax deductions probably are the last thing on your mind.

But they’re worth considering because the deduction for charitable gifts can allow you to give more.

Think you can afford to give $500? Make that $667. That’s because a person in the 25 percent tax bracket would receive a $167 tax deduction on a $667 donation, reducing the actual cost to $500.

The arithmetic is easy: $500 divided by 0.75 equals $667. The 0.75 figure comes from 1.0, representing your income, minus 0.25, representing your tax bracket.

Contributions made before 2004 ended can be deducted on the tax return due in April. Those made in the new year will be reported on the 2005 tax return.

Your tax bracket depends on income and various deductions and credits, and it only can be figured by doing a tax return.

Unless you’re accustomed to getting a big tax refund or writing a big check for taxes due, you can get a rough idea of your tax bracket from your paycheck. Compare the federal income tax withholding with your gross pay.

Most people are taxed at between 15 and 25 percent of income. (Presumably, the tax brackets for 2005 will be close to those of 2004.)

To get a charitable-gift deduction, you must itemize your tax return. For donations of less than $250, a cancelled check, credit-card statement or cash receipt is sufficient documentation of the gift. A written receipt is required for larger donations.

Many charities accept noncash gifts such as shares of stock, and this is a good way to stretch your donation even further.

If you sell the shares and then donate the proceeds, you will owe capital gains tax on the profits realized with the sale. That will leave you less to give.

But by donating the shares themselves, you avoid the capital gains tax and thus have more to give.

Your deduction will be based on the shares’ market value when the donation is made. The charity or relief organization you select can tell you how to make a gift of securities.

The gift of stocks

The American Red Cross, mounting one of the biggest tsunami-relief efforts, accepts stock. For instructions, look on its Web site, www.redcross.org, or call (800) 435-7669.

What if you plan to raise money from an investment that has lost value in the time you’ve owned it?

In that case, it’s better to sell the investment and give the cash. This way, you’ll get the tax deduction for a capital loss on top of the deduction for a charitable contribution.

Imagine you’d bought a block of shares some years ago for $1,000 and they are now worth $500. Regardless of whether you give the shares themselves or sell them and give the cash, the gift will be worth $500. That will entitle you to a $125 tax deduction, assuming a 25 percent tax bracket.

By selling the shares, you can declare a $500 loss on the investment. At the maximum capital gains tax rate of 15 percent, that will save you $75 in taxes. Adding that to the gift along with the $125 tax deduction for a charitable contribution would boost your total donation to $700.

Under some conditions, savvy taxpayers with investment losses can get deductions based on their income-tax brackets as high as 35 percent. Check with your tax preparer.

Matching donations

A couple of other thoughts on giving to relief efforts:

Double your gift. Some companies, such as General Motors and Home Depot, are matching their employees’ donations, turning every $1 given into $2. Among the most generous is Verizon, which gives $2 for every $1 from employees.

If your employer doesn’t do this, maybe you know someone whose company does. By giving your friend money to donate, you’ll pass up a tax deduction you’d get making a gift in your own name — but you’d do more for the disaster victims. Of course, you and your friend could work out a way to share the tax benefit.

Steer your business. Some companies are matching customers’ contributions. Best Buy, for example, will give $1 for every $1 contributed by a customer, through the end of this month. Donations can be made at the stores. Starbucks will contribute $2 for every pound of Sumatra coffee beans purchased at its stores.

Do homework. Be sure to check out any relief organization you’re not familiar with. The nonprofit outfit Charity Navigator rates organizations based on their financial filings and other information. Ratings are available on the Web site: www.charitynavigator.org.

Another nonprofit, GuideStar, has a list on its Web site of organizations providing tsunami relief — www.guidestar.org.